One problem in ink-jet printing is that some applications require a large supply of ink. For example, "large format" applications use large size printing media (for example, 22 inch.times.34 inch, 34 inch.times.44). Examples of large format applications include computer aided design (engineering drawings), mapping, graphic arts, and posters. The large format printed image can use a large amount of ink either because of the large printed area needing to be covered with ink or the use of 100 percent filled-in image areas, or both. Therefore, it is desirable to have ink reservoirs that contain a large amount of ink to avoid replacing an empty ink reservoir in the middle of a printing cycle or the frequent changing of the ink reservoir between printing jobs.
However, merely increasing the size of the ink reservoir in an on-board system to hold more ink has not proved to be an acceptable solution. The ink reservoir is supported on the printer carriage and moves with the printhead. Increasing the amount of ink in motion would necessarily require an increase in the size and weight of the structure that supports and moves the carriage back and forth. The increased mass of the carriage would also significantly increase the cost of the printer (for example, larger and more expensive electrical motors).
In response, recently, relatively large ink reservoir systems have developed in which the reservoir is mounted off-board.
In contrast to on-board reservoirs, printing systems using off-board ink reservoirs require means for delivering the ink from the off-board ink reservoir to the printhead. Pumps can be used for such delivery, but such pumps have problems associated with their use. For example, the ingredients in the ink can be incompatible with the pump components, and such components as diaphragms and seals can degrade when exposed to the ink solvents for extended time periods.
A second problem in ink-jet delivery arises in color printing. Color printing typically uses multiple ink reservoirs, each containing ink of a different hue. Since each ink reservoir must be individually pressurized, multiple pumps can be used. However, the addition of each additional pump increases the cost of the overall printing system. Thus, it would be desirable to use one pump that can provide the necessary pressure for all the ink reservoirs individually.
One other problem in ink-jet technology is that the customers have different purchasing criteria. Some customers, with high ink usage rate, may prefer the lower, "unit price" of a large ink reservoir. Other customers, may prefer a lower, "start-up" price of a smaller ink reservoir. Thus, it would be beneficial for the customers to have a printing system that is adaptable to ink reservoirs with different sizes. In addition, the manufacturer also benefits when the size of the ink reservoir is not a limiting factor in the design of the printer or the ink delivery system.